The present invention relates to an intake air amount controlling apparatus for an internal-combustion engine (which will be hereinafter referred to as an “engine”) that comprises a throttle valve in an intake passage for controlling the amount of intake air into the engine.
An intake air amount controlling apparatus that is capable of generating a tumble flow in a cylinder has been proposed so as to improve the fuel efficiency and the combustibility of the engine. Japanese Patent Application Publication No. H08-312358 discloses an intake air amount controlling apparatus in which a bore of a throttle valve is formed to have a curved surface and in which a main passage having a larger cross section and an auxiliary passage having a smaller cross section are separated by a partition that is placed immediately downstream of the throttle valve. When an engine load is low, the main passage is closed by one half of the throttle valve that contacts the curved surface of the bore, and the auxiliary passage is opened by the other half of the throttle valve. Thus, an air flow that passes through the auxiliary passage is biased to one direction inside an intake port, thereby generating a tumble flow within a cylinder. When an engine load is high, one half of the throttle valve leaves the curved surface of the bore so that the main passage is opened.
According to the above technique, the fuel efficiency and the combustibility can be improved with a simple structure while suppressing the cost because a tumble flow can be generated by a throttle valve without using a special mechanism.
However, according to the above technique, because the bore of the throttle valve is formed to have a curved surface so as to generate a tumble flow, the cross sectional area of the intake passage at the upstream of the throttle valve is smaller than the cross sectional area at the upstream end of the intake port of the cylinder head. Furthermore, because a partition is placed downstream of the throttle valve, the cross sectional area of the intake passage at the downstream of the throttle valve is also substantially smaller than the cross sectional area at the upstream end of the intake port of the cylinder head. Accordingly, depending on the operating condition of the engine, the amount of air passing through the throttle valve may be insufficient with respect to the amount of air entering the intake port of the cylinder head. As a result, the amount of air that is actually introduced into the cylinder may be insufficient with respect to the amount of intake air amount requested by the engine. A larger amount of intake air is requested by the engine when an engine load is high or when an engine rotational speed is high. In such a situation, the design of the above cross sectional areas may fail to introduce a desired amount of intake air into the cylinder. Moreover, a partition placed downstream of the throttle valve according to the above technique may be a resistance against the air flow toward the intake port, which may prevent a desired amount of intake air from being introduced into the cylinder.
The present invention aims at solving the above-described problems. Thus, it is one object of the present invention to propose an intake air amount controlling apparatus structured to prevent a shortage of an intake air amount introduced into a cylinder of an engine even in the operating condition where a larger amount of intake air is required.